feat: implement RPO hash using SVE instructions

[gswirski]

This PR addresses #158. It improves performance of the RPO hash function by leveraging SVE instructions on compatible ARMv8+SVE hardware. On the current generation of Amazon Graviton3 processors, I'm measuring 37% improvement against the baseline commit 90dd3ac (AWS c7g.medium instance).

To leverage SVE implementation, code needs to be compiled with --features arch-arm64-sve. Due to high latency of vector operations, only 2/3 of array elements are processed using SIMD. The rest can be processed for "free" using scalar instructions and masking the latency.

Below cargo bench --features arch-arm64-sve improvement against the baseline cargo bench.

Checklist before requesting a review

• Repo forked and branch created from next according to naming convention.
• Commit messages and codestyle follow conventions.
• Relevant issues are linked in the PR description.
• Tests added for new functionality.
• Documentation/comments updated according to changes.

[bobbinth]

Awesome work! Thank you! I'll do a full review over the next couple of days - but I did ran the benchmarks on Graviton 3 and can confirm that I'm getting the same improvement. Very cool!

[bobbinth]

Looks great! Thank you again! I left a few small nits inline and also one comment about adding a couple of Rust-based tests.

One other thing I'm thinking about is how to fix the CI (we run tests with all-features enabled). As far as I can tell, Graviton3 does not expose a feature flag to identify the SVE feature. One way to get around this is to assume that if the architecture is arm64 and OS is linux, then we are on Graviton3 - but it feels a bit hacky. Another way is to modify how we run CI tests - but I'm not sure how yet.

Any thoughts on this?

[gswirski]

Another way is to modify how we run CI tests - but I'm not sure how yet.

I would suggest replacing --all-features with manually listing all features except for arch-arm64-sve.

[bobbinth]

All looks good! Thank you!